Optical assembly

ABSTRACT

An optical assembly has a number of optical fibres ( 7 ) which terminate at connectors ( 3 ) which connect to short lengths of optical fibre ( 11 - 18 ) which connect in turn to an optical back plane ( 4 ) mounted within a housing ( 1 ). It is desirable to withdraw the connectors ( 3 ) from the housing ( 1 ) for inspection. A plurality of movable guides ( 26 ) are provided for the short fibres ( 11 - 18 ) to determine a number of optical paths which remain of constant length as the connectors are withdrawn from the housing.

[0001] This invention relates to an optical assembly, and is concernedwith the mounting of terminations of optical fibres in a manner whichpermits their visual inspection. Optical fibres are used for thetransmission of data and telecommunications and the like, and a largenumber of individual optical fibres are required to be terminated inequipment associated with a switch or other node at which the opticalinformation is to be processed, eg by way of routing to its destination,combining with other information in a multiplex fashion or by switchinginformation from one optical carrier wavelength to another.

[0002] The optical connections are housed within an enclosure, and inpractice many such optical connections may need to be housed within acommon enclosure. In the event of a fault in the optical system, or forregular maintenance, it is highly desirable to locate the opticalconnections in a manner which facilitates their inspection and checking.This is difficult if the optical connections are mounted within anequipment enclosure, such as a large cabinet or rack.

[0003] The present invention seeks to provide an improved opticalassembly.

[0004] According to this invention an optical assembly includes aplurality of optical connectors mounted in a fixed physical relationshipwith each other; a housing within which the connectors are normallyhoused and from which they can be withdrawn to permit inspection; aplurality of optical fibres each terminating at a respective one of theoptical connectors; and a plurality of movable guides which determine aplurality of optical paths, each of the same path length, for theoptical fibres, the guides being of fixed spacing and orientationrelative to each other and being movable both with respect to saidconnectors and said housing so as to maintain said path lengthsubstantially constant as the connectors are withdrawn from saidhousing.

[0005] Preferably the plurality of movable guides are movable along acurved line as the connectors are withdrawn from said housing, the linebeing curved so as to maintain said path length substantially constant.

[0006] Preferably again the line is curved so as to approximate an arcof a parabola. Over a sufficiently short arc of a parabola having ashallow curvature, the arc approximates to that of a circle. Inpractice, an arc of constant radius is satisfactory provided that thelength of the arc is short in relation to the radius.

[0007] The invention is further described by way of example withreference to the accompanying drawings, in which:

[0008]FIG. 1 illustrates an optical assembly in accordance with theinvention, in which optical connectors are located within a housing, and

[0009]FIG. 2 illustrates the optical assembly in which the opticalconnectors are shown in their withdrawn position.

[0010] Referring to FIG. 1, there is shown therein an optical assemblyforming part of communications equipment and consisting of a housing 1,having a front surface 2 carrying eight optical connectors 3, a backsurface which defines an optical back plane 4, two end faces 5, 6, andtop and bottom surfaces (not shown). If the assembly forms part of alarger equipment, some of these surfaces can be omitted.

[0011] Information such as data or telephony is carried to or from eachconnector 3 via optical fibres 7. Each fibre 7 will link to othercommunications equipment, and in practice, these fibres 7 may be manykilometres in length. The fibres 7 terminate at the connectors 3 whichare mounted in readily accessible positions at the front of the housing.The optical back plane 4 includes electro-optical components oroptical-optical components which permit optical signals to be processedby way of switching, multiplexing or the like, and fibres 11-18 areprovided linking each of the connectors 3 to the optical back plane 4.Although each fibre 11-18 may be a short length of fibre opticallycoupled to the optical back plane 4 by means of additional opticalconnectors (not shown), typically the ends of the fibres 11-18 remotefrom the connectors 3 form an integral part of the optical back plane 4where they are routed as necessary and terminated at the appropriateoptical component. Because fibres 11-18 form an integral attachment withthe optical back plane, replacement of a fibre would be an expensive anddifficult process.

[0012] A plate 19 is fixed to the front surface 2, and it supports afirst set of eight curved guides 20 which are fixed to the plate 19. Theplate 19 is provided with two curved slots 21, 22 in which are mountedrespective pegs 23 and 24 which are attached to a further plate 25 whichcarries a second set of eight further curved guides 26. The pegs 23 and24 are slidable along respective slots 21, 22.

[0013] A third set of curved guides 27 is mounted in a fixedrelationship with the housing 1, and hence the back plane 4. A pair ofrigid arms 28, 29 link the pegs 23, 24 to pivotally mounted attachmentpoints 30, 31 on the housing 1.

[0014] The three sets of curved guides define optical paths for each ofthe fibres 11-18 from the connectors 3 on the front surface 2 to theoptical back plane 4.

[0015] To permit visual inspection of each optical connector 3, thefront surface 2 on which they are mounted can be withdrawn from thehousing 1. The plate 19 which is attached to the front surface 2 isslidably mounted in the housing, so that the plate 19 can be partiallywithdrawn, as shown in FIG. 2. The connectors 3 are now clear of thehousing 1, and so can easily be checked and inspected for faults.

[0016] Clearly, the guides 20 which are mounted on the plate 19 movewith the front surface 2 and the connectors 3 when they are withdrawnfrom the housing.

[0017] From FIG. 2, it can be seen that as the connectors 3 arewithdrawn from the housing 1, the pegs 23 and 24 are constrained by thepivotally mounted arms 28, 29 to slide along the slots 21, 22 and tothereby move the second set of guides 26, so as to alter the paths ofthe optical fibres 11-18.

[0018] The slots 21, 22 are so curved as to ensure that the path lengthsof the optical fibres remain substantially constant as the connectors 3,and the plate 19 are withdrawn from the housing 2.

[0019] The slots 21, 22 take the form of a short arc of a paraboliccurve, but as the slots are short they approximate to an arc of a circleof large radius.

[0020] It will be understood that the second set of guides 26 moverelative to both the first and third sets of guides, the position of thesecond set being determined by the slots 21, 22 and by the arms 28, 29.By selecting the lengths of the arms 28 and 29 in relation to the shapeof the slots 21 and 22, the fibre paths of substantially constant lengthcan be achieved. This is important as the optical fibres are fragile andeasily damaged, but are expensive to replace.

1. An optical assembly including a plurality of optical connectorsmounted in a fixed physical relationship with each other; a housingwithin which the connectors are normally housed and from which they canbe withdrawn to permit inspection; a plurality of optical fibres eachterminating at a respective one of the optical connectors; and aplurality of movable guides which determine a plurality of opticalpaths, each of the same path length, for the optical fibres, the guidesbeing of fixed spacing and orientation relative to each other and beingmovable both with respect to said connectors and said housing so as tomaintain said path length substantially constant as the connectors arewithdrawn from said housing.
 2. An optical assembly as claimed in claim1, and wherein the plurality of movable guides are movable along acurved line as the connectors are withdrawn from said housing, the linebeing curved so as to maintain said path length substantially constant.3. An optical assembly as claimed in claim 2 and wherein the line iscurved so as to approximate an arc of a parabola.
 4. An optical assemblyas claimed in claim 2 and wherein the line is curved so as toapproximate an arc of a circle.
 5. An optical assembly as claimed inclaim 2, 3 or 4 and wherein said plurality of guides are mounted on acommon plate which is attached to said housing by a plurality ofpivotally mounted arms.
 6. An optical assembly as claimed in claim 5 andwherein said plurality of optical connectors are mounted in fixedrelationship with said common plate which has two slots each of whichdefines a said curved line, such that the ends of the arms attached tosaid common plate are slidable along said slots.
 7. An optical assemblyas claimed in claim 6 and wherein a first set of curved guides ismounted adjacent to said connectors in a fixed position therewith so asto define part of said optical paths.
 8. An optical assembly as claimedin claim 7 and wherein said plurality of movable guides constitute asecond set of curved guides-positioned between said first set and athird set of guides which is mounted in a fixed position relative tosaid housing, the first, second and third sets defining said opticalpaths.